The present disclosure relates generally to brake control valve systems for operating a vehicle's air brakes, in response to brake pipe pressure in a brake pipe, and more specifically to a brake control valve system which is insensitive to increased mechanical vibrations and brake pipe pressure fluctuations or noise.
Brake control valve systems for a vehicle having air brakes generally include a brake control valve responsive to the brake pipe pressure in a brake pipe to operate the brakes of a vehicle. For a reduction of brake pipe pressure, the brakes are proportionally applied. For an increase in brake pipe pressure, the brakes may be released totally or gradually. In the American Association of Railroads AAR system, the brake control valves include a service section and an emergency section which are responsive respectfully to a service rate of reduction and emergency rate of reduction to apply the brakes appropriately. Each section includes a separate diaphragm or piston responsive to the brake pipe pressure on one side and a reference pressure on the other. Not only must the brake control valve differentiate between a service and an emergency application, but also must react in a specific amount of time to apply the brakes and propagate the signal throughout the brake system.
Historically, the control valves have been designed to be substantially insensitive to pneumatic noise signals in the brake pipe which could cause undesired emergency (UDE) braking and undesired release (UDR). Various mechanisms have been used, for example, chokes or restrictions interconnecting the brake pipe and the reference chamber of the diaphragms, to accommodate pneumatic noise. One of the sources of the pneumatic noise or shock is the mechanical vibration of the vehicle. A major identifiable source of this mechanical vibration is in the longitudinal motion or slack action between the different cars of the vehicle or train. The insensitivity or the stability built into the brake control valves to accommodate the pneumatic noise or shock have, unbeknownst to the designers, accommodated and therefore masked, mechanically produced vibration on the brake control valve which can produce undesired minimum (UDM) service braking.
With the introduction of aluminum and other building materials as well as the modification of other portions of a car of a train, the empty car gross weight has been reduced from the range of 55,000 to 65,000 lbs. to 40,000 to 45,000 lbs. For these lighter cars, it has been noticed that the control brake valves had been experiencing an undesired minimum service application.
Experimentation has shown that the undesired minimum service application is a function of the horizontal G-forces and its duration. For a low horizontal G-force in the range of 5 to 7 Gs, typical duration of 2.6 to 2.7 milliseconds generally does not produce an undesired minimum service application. For larger residual durations, larger vertical G-forces result during the residual 4.6 milliseconds of 5.2 milliseconds producing undesirable minimum service brake application. Vertical acceleration produced by horizontal impact in the range of approximately plus and minus ±15 Gs has been observed.
This increased vertical force, that the differential motion between the service piston and the housing will cause the service piston to operate the quick service chamber check valve in the downward motion of the oscillating valve. This opening, even though for short periods of time, has been sufficient to trigger a minimum service application. Thus in addition to the previously recognized horizontal buff and draft forces, the control valve is also subjected to significant vibration and vertical shock components during slack action.
The present design provides a service valve which less sensitive to mechanically produced vibrations. The brake control valve includes a housing, a quick braking chamber and a piston subject to brake pipe pressure on one side of the piston. A bore in the housing connects the quick braking chamber at a first end and the one side of the piston at a second end. A first valve is in the housing at the first end of the bore. A first operator is in the bore for opening the first valve for a range of positions of the piston. The bore has a first portion of a first diameter and a second portion of a second diameter larger than the first diameter. The first bore portion connects the one side of the piston to the second bore portion. A first operator in the bore is connected to the piston. A seal on the first operator is dimensioned to form a seal with the first bore portion and not with the second bore portion. The seal is located on the operator to lie in the first bore portion for a first segment of the range of piston positions and to lie in the second bore portion for a second segment of the range of piston positions.
A second valve in the housing connects a brake cylinder port with a reservoir port when opened. A second operator in the housing is connected to the first operator for opening the second valve in the second segment of the range of piston positions.
The bore includes a third bore portion connecting the second bore portion to the first valve and of a third diameter and a second port is connected to the quick braking chamber. The first operator has a tip portion of a fourth diameter substantially equal to the third diameter and has an adjacent portion of a fifth diameter smaller than the fourth diameter. The tip portion has a length less than the first segment of the range.
The bore may include a tapered bore portion between the first and second bore portions and the seal lies in the tapered bore portion for a portion of the second segment of the range of piston positions.
A kit includes a bushing and a first operator which is to be connected to a piston of the brake control valve and is to extend from the piston through a bore of the bushing from a first end of the bore to a valve seat at a second end of the busing. The bore has a first bore portion of a first diameter adjacent the first end of bore and a second portion of a second diameter larger than the first diameter adjacent the second end of bore. A seal on the first operator is dimensioned to form a seal with the first bore portion and not with the second bore portion. The seal is located on the operator to lie in the first bore portion for a first segment of a range of piston positions and to lie in the second bore portion for a second segment of the range of piston positions.
The bore may include a third bore portion connecting the second bore portion to the valve seat and of a third diameter and a second port is connected and axial to the bore. The first operator has a tip portion of a fourth diameter substantially equal to the third diameter and has an adjacent portion of a fifth diameter smaller than the fourth diameter. The tip portion has a length less than the first segment of the range.
The bore may include a tapered bore portion between the first and second bore portions and the seal lies in the tapered bore portion for a portion of the second segment of the range of piston positions.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings.